Public mobile radio networks, in particular 2G/3G networks, are designed to offer services in parts of the country distributed as widely as possible. In this case, a situation can occur in which the available capacity for the demanded services is not adequate in certain regions, i.e. in certain cells, and in particular when there is a high subscriber density within these regions or cells. The problem is further exacerbated by the capabilities being provided for new services with wide bandwidths, such as multimedia, by means of the mobile access systems to the Internet, for example by means of the packet data service GPRS (General Packet Radio Service) in mobile radio networks based on the GSM Standard or UMTS (Universal Mobile Telecommunications System).
The problem is worse in locations and buildings such as airports or exhibition halls, in which it can generally also be assumed that the subscribers are moving at a relatively slow speed. In this case, by way of example, the two approaches described in the following text could lead to a solution to this problem.
It would be feasible to install very small cells, that is to say microcells or picocells, using the same technology as the overall network, for example in conjunction with overlay or umbrella cells. With this procedure, the subscriber would not notice any sign of the intervention, i.e. the installation of additional cells in the overall network, i.e. the installation would be completely transparent to the mobile radio network subscribers. Furthermore, the installation of such very small cells would fit seamlessly into the operating concept of the mobile radio network operator. There would be no transmission losses or undesirable interruptions in transmission. Furthermore, in general, no special measures would be required for charging and/or authentication of the corresponding mobile radio network subscribers. However, the installation of such very small cells in the overall system would be very expensive, involving very expensive radio technology since a very high degree of mobility is supported. Furthermore, possibly, the network could be heavily loaded with signaling traffic, since the small cells would lead to a large number of handovers between the cells. In this case, the radio technology could be constrained by its limits, in particular with regard to the transmission frequencies.
Furthermore, it would be feasible to install an alternative wire-free access system to the Internet. By way of example, this could be a wireless LAN (Local Area Network), Bluetooth or similar systems. The advantage in this case would be that it would actually create additional transmission capacity. Furthermore, the installation of such alternative systems is in general not as costly as the installation of very small cells that have been mentioned. However, one disadvantageous feature is the fact that seamless handovers from the 2G/3G mobile radio network to the alternative mobile radio network would be impossible, or feasible only to a restricted extent. This means that losses and interruptions in the transmission could occur. In a situation where, for example, the WLAN (Wireless LAN) is associated with a different network operator than the 2G/3G mobile radio network, the subscriber must authenticate himself for a second time with the WLAN, i.e. the installation of an alternative mobile radio network is not transparent to the subscriber. If, on the other hand, the WLAN is operated by the same network operator as the 2G/3G mobile radio network, then this network operator would at least have to introduce new methods for authentication and for charging for operation, and this would increase the operating costs of the system.
Until now, solutions on IP layers have normally been chosen, in order to create heterogeneous mobile radio systems such as a combination of a 2G/3G mobile radio network with a WLAN, providing IP traffic. The expression IP layer in this case refers to protocols in the Internet Protocol (IP) family which are independent of the transmission technique (for example LAN or WAN) and the access technique (mobile radio, landline network). One of the most widely discussed solutions in this case is mobile IP corresponding, for example, to RFC2002 for IP-v4. The Internet access in 3GPP 2G/3G networks is generally provided on the basis of 3GPP TS23.060. Access nodes (GGSN: Gateway GPRS Support Nodes) are in this case provided which in each case provide access to the Internet and support the appropriate Internet Protocol (IP). In this case, a fixed reference point for the Internet is provided at the GGSN, at which each subscriber can be accessed using an IP address. Within the core network, that is to say within the actual mobile radio network, the mobility between the access network nodes (GGSN) and the existing service network nodes (Service GPRS Support Node: SGSN) is provided via GTP tunneling. The entire connection between a mobile terminal (MT) and the access node GGSN together with the control data that describes the connection is referred to as a packet data protocol (PDP) context. A subscriber can be accessed by corresponding subscribers via a fixed IP address which is made available to him, for example, by an Internet Service Provider (ISP). When this subscriber now registers in a 2G/3G network, he is provided with a preferably dynamic IP address by an Internet Service Provider. In this case, this Internet Service Provider and the mobile radio operator of the 2G/3G network may be organizationally identical. The following procedure would be required for a subscriber to change between the 2G/3G network and the WLAN by means of mobile IP: the subscriber must register with his home agent in the Internet from the 2G/3G mobile radio network using his IP address. This Home Agent (HA) may be provided by a second (home) ISP. The subscriber can be accessed at this HA via a fixed IP address or via some other identification in the network of the second ISP. The data packets are then tunneled via a mobile IP (MIP) tunnel from the home agent to the access node GGSN for the IP address for the subscriber in the 2G/3G mobile radio network. In order to ensure that the packets are passed to the mobile terminal (MT) of the subscriber, a foreign agent (FA) must be provided in the GGSN in order to cancel the encapsulation of the packets tunneled to that GGSN and to send them to the mobile terminal with a fixed associated home address. When the subscriber registers in the WLAN and there is likewise a foreign agent (FA) in a WLAN controller which is acting as the access node to the Internet, then the home agent in the Internet can also pass on the packets by means of mobile IP (MIP) directly into the WLAN controller. The advantage of this solution is that the subscriber can keep his IP address when changing between systems, so that there is no need to interrupt many applications. However, as already mentioned initially, it has the disadvantage that new methods and/or measures for access authorization control and charging would need to be introduced or implemented in the area of the WLAN. If the possibility of changing between the two mobile radio networks and the two access systems, as described here between a 2G/3G mobile radio network and a WLAN, were to be offered as a service by the network operator of the 2G/3G mobile radio network, this operator would also have to provide the home agent as well as home IP addresses for his subscribers. This is because the home agent controls and provides routings for the packets to the MT. Furthermore, the subscriber identifications and charging data for the respective networks must be correlated. This therefore leads to considerable operator complexity. Furthermore, it would possibly lead to longer switching times owing to the protocol, because registration data and authentication data would need to be interchanged between the MT, FA and servers for authentication, authorization and charging (AAA) and HA. Furthermore, longer switching times can result if there is a long distance between the home agent and the local area networks in which the mobile subscriber is located.
WO 00/76145 A1 discloses a heterogeneous mobile radio system, with a GPRS network being connected to a local network and in which case GPRS services can be made accessible to the local area network by means of a specific network element.